It is a good idea to have your financing in place before you begin looking for your home. That way you can negotiate arrangements with your builder in full confidence and without delay.
A pre-approved mortgage is preliminary approval by the lender for a mortgage up to a certain amount, usually with a guaranteed rate for a specified number of days (90 days and sometimes longer). If interest rates go down during that period, you will get the benefit of the lower rate. If they go up, your rate stays locked in.
Pre-approved mortgage financing is simple to arrange, costs nothing and does not obligate you to go ahead with the loan, if you choose not to. The final mortgage amount and terms will be determined once you have reached a final agreement with your builder.